This application claims benefit of Japanese Patent Application No. 2002-063655 filed on Mar. 8, 2002, the contents of which are incorporated by the reference.
The present invention relates to image input apparatuses and, more particularly, to image input apparatuses for inputting monochromatic or color images of parts of mails illuminated from an illumination light source for sorting the mails with image recognition.
This type of image input apparatus is in actual use in a state that it is mounted in apparatuses for sorting out letters (such as postal cards and standard-size mails) and also postal matter called flat mails (the apparatuses being called letter sorter and flat mail sorter, respectively). In these sorters, an image input apparatus reads out images of mails, and succeeding stage recognition processor reads out destination names written on the mail surfaces. As a result of this reading, the mails are sorted out and accommodated in sorting boxes for respective distribution areas. Prior art techniques of this kind, for automatically reading out names of postal matter or the like, are disclosed in Japanese Patent Laid-Open No. 2001-243458, Japanese Patent Laid-Open No. 63-189978, Japanese Patent Laid-Open No. 2-171883, Japanese Patent Laid-Open No. 9-131573 and Japanese Patent Laid-Open No. 10-187952.
Compared to letters, flat mails are in a wide thickness range from small thickness to large thickness (of 50 mm at maximum), and are also in a wide area range up to a maximum size of 400 mm vertical and 300 mm horizontal. Accordingly, in image input apparatuses for flat mails, the optical system is designed such as to ensure broader field of view and greater depth compared to those in the case of letters.
Postal matter called pack mails are of sizes greater than those of flat mails, for instance one of 600 mm maximum height, 500 mm vertical and 600 mm horizontal. In view of the sorting of mails with image recognition, a sorter for pack mails (hereinafter referred to as pack mail sorter) has to meet ten or more times the thickness requirement for the flat mail sorter.
With extension of the prior art techniques concerning the image input apparatuses for flat mails, therefore, it is difficult to meet the above thickness requirement due to limitation posed by illumination depth and scene object depth of camera (i.e., range of scene object position viewed to be in focus).